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Brake Tech Series: Now That Is Different!

Saturday, March 1, 2008 - 01:00

MOST 21ST CENTURY BRAKES look much like 20th century brakes, but then the new century is still young. Besides, looks don't always tell the full story.

To review where we are right now, most vehicles employ disc and drum brakes that apply using a technology — hydraulics — that has been in common use since the 1920s. But while we all remember vehicles whose only brake "control system" was the degree of pressure applied by the driver's foot, virtually all modern vehicles use electronic overlays to improve how the brakes apply. That's been happening — with an ever-increasing degree of electronic control — since the 1980s. And as we covered in "Lose the Juice" last October, more changes appear to be just around the corner, such as the Siemens VDO electronic wedge brake calipers that apply electrically without the use of brake fluid. So much for scrambling to find DOT4. (Actually, when master cylinders become as common as points and condensers are now, it might become a scramble to find any brake fluid.)

But might we see other changes in brake design and technology?

Actually, there already are brakes in use that break the mold. How about an at-wheel technology available now that has rewritten the definition of ceramic brakes? It's been in use since around the turn of the 21st century. These are brakes with ceramic rotors.

Don't feel bad if you haven't seen them. Ceramic rotors are, so far, available only on high-dollar, high-performance cars. Porsche is one, which offers the Porsche Ceramic Composite Brake (PCCB) system on certain 911s and on the Boxster S for somewhere north of $8,000. (As we'll see shortly, this evidently is a bargain.) We haven't seen a published take-rate for the option, though Porsche did project as much as 15 percent penetration in models offering the system when they were gearing up for production. Certain ultra-high-performance Mercedes models offer setups similar in concept, as do all 2008 Ferraris and the new Corvette ZR-1.

SPOTLIGHT ON PCCB

Some reviewers have called PCCB "worth every penny," and it's required equipment in Porsche Cup racing. Depending on model, Porsche's ceramic rotors come in either 350 mm (13.78 inch) or 380 mm (14.96 inch) diameters. Calipers are fixed, six-piston units, and they're finished in a special shade of bright yellow (of course). Porsche claims two major reasons for offering the PCCB system. Fade resistance is one (high-speed braking "second to none, with almost total fade resistance," according to company literature). The other is weight savings, as the 13.78-inch rotor weighing 11 pounds, roughly half the weight of a conventional disc. The system shaves a total of about 34 pounds from under the car (apparently the calipers and/or ancillary equipment somewhat outweigh those used with conventional brakes). Porsche calls this a major reduction in both unsprung and rotational mass. There's a side benefit, too: no disc corrosion.

As Porsche's title clearly states, these discs are ceramic composites. The rotors are semi-hollow with large cooling passages between the working surfaces, which are also cross-drilled. Base disc material is cast silicon carbide (a hard-surfaced ceramic) reinforced with carbon fiber for additional strength (silicised, in Porsche-speak) and baked in an oven at 1,700 degrees Celsius. Metal hubs are mechanically attached. Specially formulated pads must be used, and the manufacturer doesn't discuss their composition. Porsche says the ceramic brake discs immediately build up a high level of friction on application and maintain it consistently during stops, and that water does not affect braking effectiveness.

The rotors are marginally thicker than standard-issue. Cooling air enters from the inside hub and exits from the slots along the outside diameter. The discs are prominently marked for left- and right-side installation.

Porsche sells retrofit kits for models that offer PCCB as original equipment, but sit down before you read the next sentence. The kit to fit a 911 Carrera 2S weighs in at just over $17,650; this doesn't include installation! The part number is 997.044.600.63, and the kit includes the four rotors, with four loaded, six-piston yellow calipers, special brake lines and supporting brackets, as well as caliper-mounting screws.

Doing the math leads to some head scratching. How can Porsche afford to put the PCCB system in new cars for "just" $8,000 or so if the retro kit fetches over $17,000? The numbers seem to suggest the standard brakes that new Porsche buyers don't get if opting for PCCB cost about $9,000 themselves, which is more than the ultra-sophisticated ceramic-disc system. Sure, there are costs associated with handling and distributing rare parts. But maybe there's some profit built in, too?

Installing the kit sounds easier than paying for it. The new parts mate up with existing on-vehicle mounting hardware and wiring. The new brake lines attach to the existing tubing. Essentially, the changeover isn't unlike any other caliper/rotor change on similar Porsches. Be careful, though. Porsche TSBs describing the procedure (Group No. 4 from February 2004 and subsequently May 2006) include precautions to avoid damaging the rotors by hitting them against solid objects (like wheels or suspension components) or through other rough handling. It's also necessary to inform the braking system control module that the PCCB setup has been installed by programming it with an appropriate scan tool.

Can't you picture all those Porsche-owning customers lining up for you to change their brakes to PCCB? No? Well picture this: Siemens says its brake-fluid-less electronic wedge brake calipers mentioned at the top of this article are just around the corner. Combining them with ceramic discs as used by Porsche, Mercedes-Benz/AMG, Ferrari and Chevrolet would make for something entirely different from what we're used to. Sure, they would still somewhat resemble today's brakes. But caring for them would require a complete re-thinking of servicing techniques and procedures.

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